Coupling circuit



March 2, 1943. N E UNDENBLAD 2,312,827 Y coUPLING CIRCUIT i .OriginalFiled June 19, 1957 l INVENToR /v/Ls E. ym/BLAD BY ATTORNEY "Atenea Mu.2, 194s ma E. Ladenbau,

Port Jell'erson, N. Y., assignor` to Radio Corporation of America, acorporation of Delaware .original application .im

149,054., Divided ma this 1o, 1937, serial No. application Scptembei'Z5, 1941, No. 412.266

11 Claims.

K m'lhe present invention relates to`lmprovements ultra high frequencycircuits, and is a division of my application Serial No. 149,054,illedJune 19, 1937, now United States Patent 2,260,529.

AI'he invention provides, amongv other things, an improved ultra highfrequency amplifier sys-v tem which is easily balanced or neutralizedagainst self-oscillation, and .wherein only a large relativemisadjustment of one circuit component with respect to the other circuitcomponents will initiate oscillations.

g An object of the present invention is to provide an improved type ofcoupling circuit comprising a pair of lines or sections thereof inenergy coupling relation between a source of high frequency currents anda load. In the preferred embodiment of the invention, one of these pairof lines or sections of lines is constituted by a coaxial linearrangement. s

A more detailed Fig. 1 illustrates diagrammatically my im'- proved typeof ultra high frequency amplier;

Fig. 1a illustrates a very general equivalent circuit given for thepurpose of exposition; and

vice 3 located within a grounded metallic sub'- stantiaily cylindricalcontainer 2. The anode l of the amplifier device 3 is coupled to groundby means of plate 4 which is capacitively coupled to the container 2.The lament of device 3A is eiectively connected to one end of ahollow'metallic tube 5 which surrounds the lead I5 to the grid and thefilament heating leads, not shown. 'I he other part of the balancedsystem comprises a dummy circuitor artificial network, shownl within thecircular dotted line simulating the reactance condition of the electrondischarge de- Vvice and consisting of a'pair of condensers arranged inthe form of three metallic plates 8, 9 'and I0. The center plate 9simulates the grid and is connected to an input lead I 6, one outerplate ,I0 simulates theanode and is grounded at container 2, and theother outer plate 8 simulates Q description of the invention follows inconjunction with the drawing, where- 1 in more detail, there is spacingbetween the plates 8, 9 and I0 determining the capacity between theelements of the -ier 3 consists of the anode capacity between'- lchanged in phase dummy.

At a distance the 'grid circuit, the grid lead I5 for the device 3 andthe lead I6 for'the dummy are short circuited by :strap 5. VAn inputcircuit I is i'nductively coupled to the leads I5 and I6 within hollowtube 5 by means of a loop, as shown, the center of the loop beinggroundedgto prevent eventual push-push eiects in the amplier system frombeing capacitively fed back into the input circuit. The push-pusheffects hereinabove mentioned refer to the excitation that could beexbetween the wires I5, I6 and loop 'I due tocapacltive coupling. -Bygrounding loop 'I at its center, I thus prevent the loop from assuming afloating potential. It will thus be obvious that ,the input totheamplifierlsystem is in push-pull relation, while the output -is not inpush-pull relation.

Another short circuiting strap II is provided across the grid leads vI5and I6 at a distance from the open end of cylindrical conducting tube 5`equal to ha'lf the length of the operating wave, in order to simulate adirect connection between the open end of tube 5 and the leads I5 and I6insofar'as these leads are considered to be in parallel or push-pushrelation. By push-push I refer to the condition wherein bothleads I5 andI6 are and act as one conductor of such a length that at the orice ofcylinder 5 a shortcircuit eiect is obtained. Since the hollowcylindrical conductor 5 is part of the tank'circuit, the grid and thecorresponding element of the networkwill ,ride This is because the gridand the corresponding element of the network are made to have the samepotential as the shell surrounding the twowire line just as if to theshell, and thus ride.on the shell potential. The reason the grids cannotbe directly connected is because such a connection would prevent anysort of input feed.

The tank or tuned output circuit for the ampliplate 4 and the container12 and a path of uniformly distributed inductance traced over theinner-surface of container-2 andthe outer surface the lament of a liveelectron'discharge device `the container 2 tube 5. The

path of this tank circuit is traced bythe arrows on the drawing. Tuningof the l'tank circuit is accomplished by means of movable metallicsliders I2, I3 which are simultaneously adjustable (uni-controlled) overthe lengths of and tube 5.

corresponding to resonance of on top of its oscillations.

they were directly connected Output energy is 'derived from theamplifier systemY by means of connection I4 which is adjustable over thelength of tube 5.

Before proceeding with a description of the operation of the push-pullamplifier system, lt should be noted that the use of a dummy or articialnetwork is essential to the operation of the particular systemillustrated in the drawing, otherwise it would not be possible to deriveoutput energy from the tube 5. Since both the cathode of device 3 andthe corresponding connection for the dummy from plate 8 are connected tothe same location on the tube 5, it should be evident that the hollowsleeve-like tubular element 5 would be at neutral potential and thecurrents would flow in the same direction in these filament connectionsif a live electron discharge device were substituted for the dummy orartificial network. Thiswill be' more apparent from a consideration ofFig. la, which illustrates in a very general manner the equivalentcircuit of Fig. 1, except for the omission of any reference to thearrangement for short-circuiting the push-push oscillations. Theelements oflFig. 1a corresponding to those in Fig. A1 have Ybeen giventhe same reference numerals except for a `prime designation. Thefilament to grid and the grid toanode capacities of the electrondischarge device have been designated in Fig. 1a as F-G and G-P,respectively.

posed on the filament connections without prohibiting neutralizing orbalancing. Putting it another way, any potential (such as from pushpullexcitation), in addition to the shell potential, will under correctphase condition add up with the shell potential. The in phase conditionofthe grid with the -ii1ament is intrinsic with theresponse of the tube3 tothe excitation it receives. Since the plate or anode is grounded,the filament is in phase with the grid; the lament excites the shell andthe grid rides on the shell. signals to the two leads I5 and I6, lead`I5 going to the grid of the grounded'anode amplifier `3 and lead I6going to the condenser group of the dummy simulating the characteristicsof the device 3. The spacings between plate 9 and plates 8 and I0 arevariable in nature to provide any desired degree of neutralization orbalance. The excitation introduced on leads I5 and I6 by input circuit1causes device 3 to pass electron cur- 'rent which causes the filamentof the electron discharge device to oscillate.. The inductive couplingbetween' input circuit 1 and leads I5 and I6 minimizes back reaction.Slider or strap 6 across the leads I 5 and I6 tunes these circuitconnections in push-pull relation. The strap Il In Fig. 2, theconnections to the grid of device The input circuit 1 supplies push-pull3 and plate 9 of the dummy comprise portions o! parallel hollow tubesI5" and I6" which are 100% coupled to the loop, shown in dotted lines,connected to input circuit 1. The currents in tubes I5" and I6 flow onthe outside of these tubes from the grid of device 3 and plate 9 to theapertures I1 through which the input loop passes, and through theapertures to the inner surface of the tubes down to the input circuit.The arrows indicatethe directions of the currents and the surfaces onwhich they flow. The input loop is here perfectly shielded andso coupledto the lines I5l and IB" that the original input lines 1 for push-pulloperation form a perfectly continuous connection all the way to the gridand plate 9; the only requirement being that the loop from apertures I1to bridge 25 be onequarterjwavelength long and the surge impedance oftheinner conductors be equal to the surge impedance between its shells. Thequarter wavelength distance indicated in Fig. v2 provides a highimpedance for currents onthe upper outside part of tubes I5" and. I6which tend to flow 1. A coupling circuit for use between a source n I ofhigh frequency currents and a load, comprising a section oftwo-conductor line each conductor of which is hollow, an electricallyconducting bridge connected across said conductors, each conductor ofsaid line having an aperture therein located from said bridge a distanceequal to an odd multiple including unity of one-quarter wave-length atthe operating `frequency, and another section of two-conductor linepassing through said apertures and in energy transfer relation to saidfirst section of line, said load being connected 'to one of said linesections and said source being connected'to .the other of said linesections.

2. A coupling circuit for use between a source of high frequencycurrents and a. load, compris, ing a section of two-conductor line eachconductor of which is hollow, an electrically con- -ducting bridgeconnected across said conductors,

tunes the leads I5 and IB in push-push so that the push-push drop iszerowhere the leads I5 and I6 emerge at the open' end of tube 5, or witha controllable amount (either inductive or ca.-

pacitive) as the need of the circuit requires. In' this wav, there isobtainedaontrol of the regeneration which can offset the "degenerativeeffect of the steady capacitive drop through the filament to grid andgrid to anode capacities of device 3. In Fig. 2 all back reaction orcapacity push-push feed back eiect has been eliminated due to the use ofdouble concentric lines.

each conductor of said line having an aperture therein located from saidbridge a distance equal to an odd multiple including unity ofone-quarter wave-length at the operating frequency, said distances beingequal, and anothersection of two-conductor line passing through saidapertures and in energy transfer relation to said flrst section of line,said load being connected to one of said line sections and said sourcebeing connected to the other of said line sections.

3. A coupling circuit for use between a source of high frequencycurrents and a load, comprising a section of two-conductor line eachconductor of 'which is hollow, an electricaily conducting bridgeconnected across said conductors. each conductor of saidv line having anaperture therein located from said bridge a distance equal 'to an oddmultiple including unity of one-quarter wavelength atthe operatingfrequency, and another section of two-conductor line whose conductorsextend into the interior of the hollow conductors of said first line andconnect together through said apertures. said loadbeing proximately anodd multiple connected to one of said line'sections and said Asourcebeing connected to-the other of said line sections.

40A coupling circuit for use between a source of high frequency currentsand a load, comprising a section of two-conductor line eachconductor ofwhich is hollow,

an electrically conducting v .bridge connected across said conductors,each conductor of said line having an aperture therein located from saidbridge a distance equal to an odd'multiple including unit of one-quarterl wavelength at the operating frequency, and another sectionV oftwo-conductor line whose conductors extend into thev interior of thehollow conductors of said first line and connect together through saidapertures, said source and said load being connected to said second andfirst sections of line respectively, on opposite sides of saidapertures. whereby the currents in said second line flow over only thatportion of the outside of the conductors of said rst load and saidapertures.

5. A coupling circuit in accordance with claim 1 characterized in this,that said bridge is adjustable in position over` the conductors of saidrst section of line.

6. A couplingcircuit between a source of high line between ytheproximately an odd multiple including unity oi a A frequency currentsand a loadcomprising a pair of physically parallel tubular conductorshaving acljacently 'located 'apertures therein, leads ex tending withinsaid tubular conductors and connected together through said apertures. ashortcircuiting element bridging said pair of tubular conductors at alocation approximately an odd multiple including unity of a quarterwavelength at the operating frequency from said apertures.

said source and load being connected to said tubular conductors and ofsaid apertures.

7. A coupling circuit between a source of high leads on opposite sidesfrequency currents and a load, comprising a pair of physically paralleltubular conductors having adjacently located apertures therein, leadsinsulatingly extending within said tubular con-` ductors and connectedtogether through said apertures, a short-circuiting element bridgingsaid pair of tubular conductors at a location apincluding unity of aquarter wavelength at the operating frequency from said apertures, saidsource and load being.

a quarter wavelength at the operating frequency from said apertures,said source and load being connected to said tubularv conductors andleads on opposite sidesof said apertures. said load including a pair ofstructures of similar capacitive characteristics, one element of onestructure of said pair being connected to a point on one oi' saidtubular conductors, and a corresponding element of the other structureoi said pair being connected to a point on the other tubular conductor,both of said points being substantially equally distant from saidapertures.

9; A coupling circuit between a source of high frequency currents and aload, comprising a pair of'physically parallel tubular conductors havving adjacently located apertures therein, leads insulatingly extendingwithin said tubular conductors and connected together through said'apertures, a short-circuiting element bridging said pair of tubularconductors at a location apquarter wavelength at the operating frequencyfrom said apertures, said source being connected to said leads on oneside of said apertures, and said load being connected to both of saidtubular conductors on the other side of said apertures, the distancesbetween said apertures and the points of connection on said tubularconductors to said load being equal.

10. A coupling circuit between a source of lhigh frequency currents'anda load, comprising a pair of physically parallel tubular conductorshaving adjacently located apertures therein, leads insulatinglyextending within said tubular conductors and connected together throughsaid apertures, ashort-circuiting element bridging said pair of tubularconductors at a location approximately an odd multiple including unityof a quarter wave-length at the' operating frequency from\ saidapertures, said source being connected to said leads on one side of saidapertures. and said load being connected to both of said tubularconductors at or near the ends thereof on the other side of saidapertures, thedistances between said apertures and the points of connecltion on said tubular conductors to said load being equal.

' 11. A coupling circuit between a source of high frequency currents anda load. comprising a pair of physically paralleltubular adjacentlylocated apertures therein. leads insulatingly extending within saidtubular conductors and connected together through said apertures, ashort-circuiting element bridging said pair of tubular conductors at alocation approximately an odd multiple including unity of a quarterwavelength at the operating frequency from said apertures, said sourceand load being connected to said leads and tubular conductors.respectively, on opposite sides NILB E. IINDENBLAD.

conductors having of said apertures.

